CIS 460 – Network Analysis and Design

1. CIS 460 – Network Analysis and Design Chapter 3 – Characterizing the Existing Internetwork

2. Characterizing the Existing Network • Examine the customers existing network to better judge how to meet expectations for network scalability, performance and availability • Understanding the existing network’s structure, uses, and behavior you get a better feel if the design goals are realistic • Most designers design network enhancements to existing networks

3. Characterizing the Network Infrastructure • Develop a network map • Learning location of major internetworking devices and network segments • Documenting the names and addresses of major devices and segments • Documenting the types and lengths of physical cabling • Investigating architectural and environmental constraints

4. Developing a Network Map • Location of major hosts, interconnection devices and network segments • Help understand traffic flow • Data on performance characteristics of network segments coupled with location information gives insight to where users are concentrated and the level of traffic to be supported • Goal is to obtain a map of the already-implemented network

5. Tools for Developing Network Maps • Invest in a good network-diagramming tool • Visio is one example • Some companies offer diagramming and network documentation tools that automatically discover existing networks.

6. What Should a Network Map Include? • Geographical – countries, states, provinces, cities and campuses • Wan connections between countries, states, and cities • Buildings and floors and rooms or cubicles if possible • WAN and LAN connections between buildings and campuses

7. What should a network map include? (Cont’d) • Indication of the data-link technology for WANs and LANs • Service provider for WANs • Location of routers and switches • Virtual Private Networks • Major servers or server farms • Location of major network-management stations • Location and reach of any virtual LANs

8. What should a network map include? (Cont’d) • Topology of any firewall security system • Location of any dial-in and dial out systems • Indication of where workstations reside • Depiction of the logical topology or architecture of the network

9. Characterizing Network Addressing and Naming • Documenting any strategies customer has for networking addressing and naming • On detailed network maps include the names of major sites, routers, network segments and servers • Investigate the network-layer addresses your customer uses • A customer goal might be to use route summarization • Existing addressing scheme might affect the routing protocols you can select

10. Characterizing Wiring and Media • Document existing cabling design to help plan for enhancements and identify any potential problems • Assess who well equipment and cables are labeled • Document connections between buildings (number of pairs of wire and type) • Locate telecommunications wiring closets, cross-connect rooms and any lab or computer rooms • Use the chart in Table 3-1 on page 61.

11. Checking Architectural and Environmental Constraints • Pay attention to environmental during cabling investigation • Flooding, right of way issues, heavy equipment usage • Building issues

12. Checking the Health of the Existing Internetwork • Knowing baseline of existing system give a standard to measure new system against • Existing segments will effect overall network performance • Segments that will interoperate with new segments, backbone networks and networks that connect old and new areas • Legacy systems may have to be included

13. The Challenges of Developing a Baseline of Network Performance • Not an easy task • Time selection • Time allocation • Typical time period • Periods of normal traffic laod • Customer may not recognize need • Need good understanding of customers technical and business goals

14. Analyzing Network Availability • Gather statistics on MTBF and MTTR • Learn about causes of the most recent and most disruptive periods of downtime • Document availability in a Table such as Table 3-2 on page 65

15. Analyzing Network Utilization • A measure of how much bandwidth is in use during a specific time interval • Usually a percentage of capacity • Different tools use different averaging windows • Use appropriate division of time • Averaged over too short or long a period can be misleading • It is always better to error on the side of gathering too much data

16. Bandwidth Utilization by Protocol • Measure by broadcast versus unicast traffic • By each major protocol • Some protocols send excessive broadcast traffic • Use a protocol analyzer on each major network segment • Relative usage specifies how much bandwidth is used by the protocol in comparison to total bandwidth currently in use by the segment. • Absolute usage specifies how much bandwidth is used by the protocol in comparison to the total capacity of the segment • Document using a Table such as 3-3 on page 69

17. Analyzing Network Efficiency • Use a bit error rate tester on serial lines to test number of damaged bits compared to total bits • On packet-switched networks measure frame errors because a whole frame is bad if a single bit is changed or dropped. Utilizes cyclic redundancy check (CRC) based on bits in a frame • A protocol analyzer can check the CRC on received frames

18. Analyzing Network Efficiency (Cont’d) • Errors increase as utilization increases so document errors as function of the number of bytes seen by the monitoring tool • Some monitors allow you to print the top 10 stations sending frames • Baseline analysis should also include upper-layer problems • Accuracy should also include a measurement of lost packets

19. Analyzing ATM Errors • Accuracy is measure in terms of cell error ration (CER), cell loss ration (CLR), cell misinsertion rate (CMR) and severely errored cell block ration (SECBR) • CER is number of errored cells divided by total number of successfully transferred cells plus errored cells • CMR is caused by an undetected error in the header of a cell • If no tool, check the performance by analyzing the level of frame errors and upper-level problems

20. Analyzing Network Efficiency • Bandwidth utilization is optimized when applications and protocols are configured to send large amounts of data per frame. • The goal is to maximize the number of data bytes compared to the number of bytes in headers and in acknowledgment packets • Use a protocol analyzer to examine the current frame sizes on the network • Analyzing frame sizes can help understand health of a network, not just the efficiency

21. Analyzing Delay and Response Time • Measure response time between significant network devices before and after a new network design is implemented • Send ping packets and measure time to send and respond • Document using a Table such as 3-4 on page 75 • Measure response time from a user point of view • Test user applications and system protocols • Do some testing when the system is experiencing problems or change

22. Checking the Status of Major Routers • Includes determining how busy the router is, how many packets the router has processed, how many packets the router has dropped and the status of buffers and queues. • You can use the Simple Network Management Protocol (SNMP) to check the health of a router • To check the health of a router you need to check the router variable on a regular basis over a few days

23. Tools for Characterizing the Existing Internetwork • Protocol Analyzers • Remote Monitoring Tools • Cisco Tools for characterizing an Existing Internetwork • Cisco Discovery Protocol • Enterprise Accounting for NetFlow • Netsys Service-Level Management Suite • Cisco Works • Other Tools

24. Protocol Analyzers • A fault-and-performance-management tool that captures network traffic, decodes the protocols in the captured packets and provides statistics to characterize load, errors, and response time. • Sniffer Network Analyzer • EtherPeek

25. Remote Monitoring Tools • Remote Monitoring (RMON) MIB developed to overcome shortcomings in the standard SNMP MIB for gathering statistics on data-link and physical-layer parameters • Gathers statistics on CRC errors, Ethernet collisions, Token-ring soft errors, frame sizes, number of packets in and out of a device, and the rate of broadcast packets • The RMON MIB alarm group allows a network manager to set thresholds for network parameters and automatically delivers alerts to management

26. Cisco Tools for Characterizing an Existing Internetwork • Cisco has a complete range of tools for characterizing an existing internetwork, ranging from the Cisco Discovery Protocol to sophisticated Netsys tools

27. Cisco Discovery Protocol • Specifies a method for Cisco routers and switches to send configuration information to each other on a regular basis • Look at information about neighboring routers: • Protocols enabled • Network address for enabled protocols • Number and types of interfaces • Type of platform and its capabilities • Version of Cisco IOS software

28. Enterprise Accounting for NetFlow • Can help understand bandwidth usage and allocation, quality of service levels, ro8uter usage, and router port usage • Recognizes network flows and characterizes network and router usage by user (IP address), application, and department

29. Netsys Service-Level Management Suite • Enables defining, monitoring, and assessing network connectivity, security, and performance. • Particularly useful for characterizing an existing network as part of a network design proposal

30. Cisco Works • A series of SNMP-based internetworking management software application for device monitoring, configuration maintenance, and troubleshooting of Cisco devices

31. Other Tools for Characterizing an Existing Internetwork • Many other tools out there. Visit various web sites identified in the book to look at some of the tools.

32. Conclusion • Use a network health checklist like the one on page 81 to assist in verifying the health of an existing network.